1. Field of the Invention
The present invention relates to a method of shearing, such as blanking and piercing, a thin metal sheet.
2. Description of the Related Art
For example, when a thin metal sheet is blanked, it is necessary to restrict the ratio of the clearance between dies to the thickness of the sheet to a predetermined value or less in conventional blanking methods in order to inhibit a blanking burr. However, when the thickness of a sheet is 0.1 mm or less, that is, approximately dozens of .mu.m or less, it is difficult to ensure the above ratio in terms of precision, particularly when a thin metal sheet is blanked by a complicatedly-shaped die. As a result, a great deal of labor and cost are required to produce and maintain the die device.
Methods of inhibiting a blanking burr are known such as a blanking method by using upper and lower blanking dies and a burr-free blanking method (Japanese Patent Laid-Open Nos. 1-293922, 3-234321 and 4-146100). They present, however, the following problems when applied to a thin sheet described above. The former method requires a special type of device (Japanese Patent Laid-Open No. 2-127997), whereas the latter method is difficult to be applied to a thin sheet.
As stated above, in the conventional methods, it is hard to blank a thin metal sheet having a thickness of approximately 0.1 mm or less while inhibiting burring without using any special type of device or blanking die.